Determinant wing assembly

ABSTRACT

A method and apparatus for manufacturing wings includes a fixture that holds wing panels for drilling and edge trimming by accurate numerically controlled machine tools using original numerical part definition records, utilizing spatial relationships between key features of detail parts or subassemblies as represented by coordination features machined into the parts and subassemblies, thereby making the parts and subassemblies intrinsically determinant of the dimensions and contour of the wing. Spars are attached to the wing panel using the coordination holes to locate the spars accurately on the panel in accordance with the original engineering design, and in-spar ribs are attached to rib posts on the spar using accurately drilled coordination holes in the ends of the rib and in the rib post. The wing contour is determined by the configuration of the spars and ribs rather than by any conventional hard tooling which determines the wing contour in conventional processes.

REFERENCE TO RELATED APPLICATIONS

This application relates to U.S. Provisional Application No. 60/013,986filed on Mar. 22, 1996 and International Application No. PCT/US97/04550filed Mar. 21, 1997, both entitled “Determinant Wing Assembly” by DavidStrand, Clayton Munk and Paul Nelson.

TECHNICAL FIELD

This invention relates to a method and apparatus for inexpensivelymanufacturing major airplane assemblies to close tolerances, and moreparticularly, to a method and apparatus for assembling wing skins,spars, ribs and other components with unprecedented precision to producea wing having close conformance to the original engineeringconfiguration, while significantly reducing tooling expense.

BACKGROUND OF THE INVENTION

Conventional manufacturing techniques for assembling components andsubassemblies to produce airplane wings to a specified contour rely onfixtured “hardpoint” tooling techniques utilizing floor assembly jigsand templates to locate and temporarily fasten detailed structural partstogether to locate the parts correctly relative to one another. Thistraditional tooling concept usually requires primary assembly tools foreach subassembly produced, and two large wing major assembly tools (leftand right) for final assembly of the subassemblies into a completedwing.

Assembly tooling is intended to accurately reflect the originalengineering design of the product, but there are many steps between theoriginal design of the product and the final manufacture of the tool, soit is not unusual that the tool as finally manufactured producesmissized wings or wing components that would be outside of thedimensional tolerances of the original wing or wing component designunless extensive, time consuming and costly hand work is applied tocorrect the tooling-induced errors. More seriously, a tool that wasoriginally built within tolerance can distort out of tolerance from thehard use it typically receives in the factory. Moreover, dimensionalvariations caused by temperature changes in the factory can produce avariation in the final part dimensions as produced on the tool,particularly when a large difference in the coefficient of thermalexpansion exists between the tooling material and the wing material, asin the usual case where the tooling is made of steel and the wingcomponents are made of aluminum or titanium. Since dimensions inairplane construction are often controlled to within 0.005″, temperatureinduced dimensional variations can be significant.

Hand drilling of the part on the tool can produce holes that are notperfectly round or normal to the part surface when the drill ispresented to the part at an angle that is slightly nonperpendicular tothe part, and also when the drill is plunged into the part with a motionthat is not perfectly linear. Parts can shift out of their intendedposition when they are fastened in non-round holes, and the nonuniformhole-to-fastener interference in a non-round hole or a hole that isaxially skewed from the hole in the mating part lacks the strength andfatigue durability of round holes drilled normal to the part surface.The tolerance buildup on the wing subassemblies can result insignificant growth from the original design dimensions, particularlywhen the part is located on the tool at one end of the part, forcing allof the part variation in one direction instead of centering it over thetrue intended position.

Wing components are typically fastened together with high interferencefasteners and/or fasteners in cold worked holes. Interference fasteners,such as rivets and lock bolts, and cold working of a fastener hole, bothcreate a pattern of stress in the metal around the hole that improvesthe fatigue life of the assembled joint, but a long line of such stresspatterns causes dimensional growth of the assembly, primarily in thelongitudinal direction, and also can cause an elongated part to warp, or“banana”, along its length. Attempts to restrain the assembly to preventsuch distortion are generally fruitless, so the most successfultechnique to date has been to attempt to predict the extent of thedistortion and account for it in the original design of the parts, withthe intent that the assembly will distort to a shape that isapproximately what is called for in the design. However, suchpredictions are only approximations because of the naturally occurringvariations in the installation of fasteners and the cold working ofholes, so there is often a degree of unpredictability in theconfiguration of the final assembly. A process for nullifying theeffects of the distortion in the subassemblies before they are fastenedinto the final assembly has long been sought and would be of significantvalue in wing manufacturing, as well as in the manufacture of otherparts of the airplane.

Wing major tooling is expensive to build and maintain within tolerance,and requires a long lead time to design and build. The enormous cost andlong lead time to build wing major tooling is a profound deterrent toredesigning the wing of an existing model airplane, even when newdevelopments in aerodynamics are made, because the new design wouldnecessitate rebuilding all the wing major tools and some or all of thewing component tooling.

The capability of quickly designing and building custom wings forairline customers having particular requirements not met by existingairplane models would give an airframe manufacturer an enormouscompetitive advantage. Currently, that capability does not exist becausethe cost of the dedicated wing major tooling and the factory floor spacethat such tooling would require make the cost of “designer wings”prohibitively expensive. However, if the same tooling that is used tomake the standard wing for a particular model could be quickly andeasily converted to building a custom wing meeting the particularrequirements of a customer, and then converted back to the standardmodel or another custom wing design, airplanes could be offered tocustomers with wings optimized specifically to meet their specificrequirements. The only incremental cost of the new wing would be theengineering and possibly some modest machining of headers and other lowcost tooling that would be unique to that wing design.

The disadvantages of manufacturing processes using hard tooling areinherent. Although these disadvantages can be minimized by rigorousquality control techniques, they will always be present to some extentin the manufacture of large mechanical structures using hard tooling. Adeterminant assembly process has been developed and is in production forairplane fuselage manufacture, replacing hardpoint tooling withself-locating detail parts that determine the configuration of theassembly by their own dimensions and certain coordinating featuresincorporated into the design of the parts. This new process, shown inU.S. Pat. No. 5,560,102 entitled “Panel and Fuselage Assembly” by Micaleand Strand, has proven to produce far more accurate assemblies with muchless rework. Application of the determinant assembly process in airplanewing manufacture should yield a better process that eliminates orminimizes the use of hard tooling while increasing both the productioncapacity of the factory and increasing the quality of the product byreducing part variability while reducing the costs of production andproviding flexibility in making fast design changes available to itscustomers. These improvements would be a great boon to an airframemanufacturers and its customers and would improve the manufacturer'scompetitive position in the marketplace. The present invention is asignificant step toward such a process.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a method ofmanufacturing large and heavy assemblies, such as airplane wings, fromflexible and semi-flexible parts and subassemblies in accordance with anoriginal engineering design, free from reliance on conventional“hardpoint” tooling to determine the placement of the parts relative toone another and the contour of the assembly.

Another object of the invention is to provide a method of manufacturingairplane wings using intrinsic features of the component parts to allowthem to self locate and determine assembly dimensions and contoursrather than using the dimensions and contours of conventional tooling todetermine assembly dimensions and contours.

It is yet another object of this invention to provide a system formanufacturing airplane wings that is inherently more accurate than theprior art and produces structures in which the parts are consistentlylocated more accurately on the structure with closer conformance to thetolerance specified by the engineering design.

It is yet a further object of the invention to provide a system formanufacturing airplane wings that is faster and less expensive than theprior art traditional techniques and requires less factory space and isless dependent upon the skill of workers to produce parts within theengineering tolerances specified.

Still a further object of this invention is to provide a method andapparatus which facilitates the manufacturing of subassemblies with aprecision and repeatability that enables airplane wings to be builtwithin tolerance specified in the original engineering wing design.

Another still further object of the invention is to provide a method forbuilding airplane wings having a sequence of operations arranged toapply critical features to the detail parts or subassemblies after thewing or wing component has been distorted by operations that distort thewing or component, such as interference fasteners.

Yet another still further object of the invention is to provide a methodof assembling a major assembly from distorted parts or subassemblies byaccommodating their distortion with a probing routine that createspartial digital representation of the distorted part or subassembly, andcompares it to the space in which it is to fit, then produces a best-fitorientation for the distorted part or assembly to minimize the effectsof the distortion.

It is yet another still further object of the invention to provide aprocess for manufacturing an airplane wing wherein only the keycharacteristics of the components and the wing are controlled, and theyare controlled only for as long as they are important, and then they areallowed to vary after they are no longer important.

These and other objects of the invention are attained in a system forassembling wings and other large, heavy assemblies from flexible andsemi-flexible subassemblies using a method that utilizes spatialrelationships between key features of detail parts or subassemblies asrepresented by coordination features such as holes and machined surfacesdrilled or machined into the parts and subassemblies by accuratenumerically controlled machine tools using digital data from originalengineering product definition, thereby making the components andsubassemblies themselves intrinsically determinant of the dimensions andcontour of the wing.

DESCRIPTION OF THE DRAWINGS

The invention and its many attendant objects and advantages will becomebetter understood upon reading the following detailed description of thepreferred embodiment in conjunction with the following drawings,wherein:

FIG. 1 is a top level schematic diagram of an assembly process forairplane wings in accordance with this invention;

FIGS. 2A-2F are schematic views of certain milestone steps in theprocess according to this invention for assembling components andsubassemblies into a wing box in accordance with this invention;

FIG. 3 is a perspective view of a portion of a wing majors assembly cellin accordance with this invention;

FIG. 4 is a perspective view one of the headers shown in the wing majorsassembly cell FIG. 3;

FIG. 5 is a schematic view of a computer architecture and process forconverting data from a digital product definition to instruction in amachine tool controller for perform certain assembly operations;

FIG. 6 is a sectional elevation showing a rib fastened between spars inan airplane wing made in accordance with this invention;

FIG. 7 is an enlarged view of a junction between a stringer, a wingskin, a rib and a spar in a section of a wing made in accordance withthis invention;

FIG. 8 is a sectional elevation of a side-of-body connection between awing and an airplane fuselage in accordance with this invention;

FIG. 8A is a perspective view of the inboard end of a wing made inaccordance with this invention showing the side-of-body fitting;

FIG. 9 is a sectional elevation of a partially assembled wing boxshowing the spars bridged by top and bottom wing panels with attachedstringers, but omitting the ribs for clarity of illustration;

FIG. 10 is a perspective view of a completely assembled wing boxaccording to this invention, omitting the side-of-body web to shown theinterior of the wing box;

FIG. 11 is an enlarged perspective view of the inboard end of the wingbox shown in FIG. 10;

FIG. 12 is an elevation, partly in section, of an edge gauge/clamp forpositioning a spar relative to the edge of a wing panel and clamping itin position;

FIG. 13 is an elevation of a temporary spar support used in the processof this invention;

FIG. 14 is an exploded view of a wing box made in accordance with thisinvention, showing a shear tied rib fastened between two spars with thewing panels exploded away;

FIG. 15 is a perspective view of a wing box in phantom, showing theplacement of engine strut fittings to the wing box;

FIGS. 16 and 17 are elevation and plan views of flap supports attachedto the rear spar and the lower wing panel;

FIG. 18 is a schematic elevation of a process for mounting aileron hingeribs to the rear spar;

FIG. 19 is a schematic illustration of a spar-based wing assemblyprocess in accordance with this invention with the wing waterlineoriented in the vertical position during assembly; and

FIG. 20 is a sectional end elevation of an apparatus for assemblingwings using a spar-based horizontal assembly process.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention is described as applied to a preferred embodiment, namely,a process of assembling airplane wings. However, it is contemplated thatthis invention has general application to the assembly of parts intomajor assemblies where adherence to a specified set of dimensionaltolerances is desired, particularly- where some or all of the parts andsubassemblies are flexible or semi-flexible.

Referring now to the drawings, wherein like reference charactersdesignate identical or corresponding parts, and more particularly toFIG. 1 thereof, top level schematic diagram illustrates the majorprocess steps in the determinant wing assembly process according to thisinvention. The process begins with building the major components of thewing, including upper and lower wing panels 30 and 32, a rear spar 34and a front spar 36, and in-spar ribs 38. The major components arebrought together on a computer numerically controlled machine tool 40and assembled as a wing in the horizontal position, as illustrated inFIG. 2, on a series of holding fixtures 42 mounted on a bed 44 of themachine tool 40. The lower wing panel 32 is positioned on the holdingfixtures 40, and the spars 34 and 36 are positioned adjacent trailingand leading edges of the lower wing panel 32. The ribs 38 are positionedbetween the spars 34 and 36 and are fastened to the spars and to thelower wing panel 32, and the spars 32 and 34 are also fastened to thelower wing panel 32. Three engine strut fittings 250 are fastened to theunderside of the wing box with fasteners extending through the lowerwing skin and into internal load fittings 48 fastened to the designatedribs, and a bearing 208 for a landing gear link 212 is attached to therear spar, along with a forward trunnion fitting 210, as shown in FIG.10. The wing is closed out by fastening the upper wing panel 30 to thefront and rear spars and to the ribs 38. The process for performingthese steps is described in detail below.

Conventional fasteners are contemplated for use in the preferredembodiment. These conventional fasteners, such as rivets, bolts, lockbolts, Hi-Locks and the like are widely used in the aerospace industry,and are well understood and reliable. However, this invention is notrestricted to the use of conventional fasteners and is fully compatiblewith the use of advanced fastening techniques such as co-curing andother bonding techniques for thermoset composite parts, inductionwelding of thermoplastic parts, as described in U.S. patent applicationSer. No. 08/367,546 entitled “Multipass Induction Heating forThermoplastic Welding” filed by Peterson et al., and friction welding ofmetallic parts as described in a PCT International Application No. WO93/10935 when these processes become sufficiently understood, reliableand proven for use in flight critical hardware.

The tooling, such as the holding fixtures 42, used in the process isprimarily for supporting the components and parts for drilling andmachining by the machine tool 40, such as a Henri Line gantry mounted5-axis tool, or a Cincinnati Milacron vertical tower 5-axis machinetool. Other machine tools of similar capabilities could also be used.The required capabilities are precision and repeatability in spindlepositioning, which in this application is about ±0.005″, and operationunder control of a machine controller that can be programmed toincorporate digital product definition data originating from anengineering authority for the wing and wing components, so thatcoordination features specified by the digital product definition can beplaced accurately and repeatably by the machine tool 40. These twocapabilities enable the machine tool 40 to apply coordination features,such as coordination holes and machined coordination surfaces, to parts,components and assemblies at precisely accurate positions specified inthe digital product definition. These coordination features are used toposition parts and components relative to each other where they arepinned and fastened, thereby eliminating or drastically reducing theneed for fixed hard tooling that previously was used to located theparts and components relative to each other. The coordination featuresthus determine the relative position of the parts and components thatcomprise the assembly, and thereby determine the size and shape of theassembly, independently of any tooling.

Wing Panel Build-up

Wing panel build-up begins with erection of the holding fixtures 42 onthe machine tool bed 44. The holding fixtures 42 can be any of amultitude of designs that will support several wing skin planks 54 whichtogether make up the lower wing skin 56. The planks 54 are supported ingenerally horizontal or lying down position, with the lower surface, or“outer mold line” conforming to the wing panel profile specified in theengineering design. The preferred embodiment of a set of holdingfixtures 42 is shown in FIG. 3. Each holding fixture includes a sturdybase structure 58 supporting a header 60 on which the wing planks 54lie, with their outer surfaces in contact with a contact pad 62 on thetop of the header 60. The contact pad 62 is a strip of durable,non-abrasive material such as ultra high density polyethylene,polyurethane, or Teflon which will support the wing planks 54 withoutdeflection under compression, but will not scratch the surface coatingon the wing skin planks 54. After the holding fixtures 42 are mountedfor the first time on the machine tool bed 44, the machine tool 40 isused to machine the contact pads 62 to the exact contour specified bythe engineering design, using the data from the digital productdefinition.

The digital product definition is the ultimate engineering authority forthe product, in this case, a particular model airplane. It exists on amaster computer 64 in a computer-aided design program as a digital model66 which includes all the dimensions, tolerances, materials andprocesses that completely define the product. The dimensional data fromthe model 66 is provided in a file to an NC programmer who uses it tocreate a dataset 68 and machine instructions, such as cutter type andsize, feed speeds, and other information used by a controller of themachine tool 40 to control the operation of the tool. The dataset andmachine instructions are launched in a post processor 70 where they areconverted to a machine readable file 72 that is transmitted to a datamanagement system 74 where it is stored for use by the machine toolcontrollers 78. On demand, the file 72 is transmitted over phone lines76 or other known means of communication to the machine tool controller78 for use by the controller in operating the machine tool 40.

The file 72 in the data management system 74 is used to program themachine tool controller 78 to direct the machine tool 40 to drillcoordination holes and fastener holes and other precision machining andpositioning operations described below. The machine tool 40 also drillsholes into the headers 60 for three precision drilled bushings 80 intowhich are set precision ground alignment pins 82 for positioning thewing skin planks 54 at a known position on the headers 60. The positionis not critical so the accuracy of the wing is not dependent on theaccuracy of the registry of the wing skin planks 54 on the headers 60since the planks are probed for their actual position on the headers 60using a contact probe 84 mounted on the machine tool 40. A vacuum source86 is energized to create a suction in a series of suction cups 88 onthe headers 60 to secure the wing skin planks 54 in position against thecontact pads 62 on the headers 60, and the contact probe 84 is moved bythe machine tool 40 to probe the key coordination features on the wingskin planks 54. A suitable probe for this purpose would be a Renishawcontact probe Model No. RW486 made by the Renishaw Company in Onendagua,N.Y., although other probes available from other sources could also beused.

After probing of the key coordination features on the wing skin planks54 to determine the actual position of the planks on the headers 60, themachine control program is updated or normalized to synchronize the dataset from the digital product definition with the actual position of thewing skin planks 54 on the headers 60. The machine program is nowinitiated to drill coordination holes in the inboard end of the wingskin planks 54 common to coordination holes drilled in the inboard endof a series of longitudinal wing stringers 90. The stringers 90 extendlongitudinally, or span-wise along the wing and serve to connect theseveral wing skin planks 54 into a single wing panel 32, and also tostiffen the panel. They also serve as the connecting structure betweenthe in-spar ribs 38 and the wing skin 56, as discussed in more detailbelow. The stringers 90 are located spanwise on the planks 54 via thecoordination holes, and the floating ends of the stringers 90 arelocated chordwise by the machine tool 40 as it progresses down theplank, drilling and fastening as it goes. The machine tool 40 can use asimple pin to engage the side of the stringer to position it chordwise,or can use a centering mechanism as shown in U.S. Pat. No. 5,299,894 orU.S. Pat. No. 5,477,596, both by Peter McCowin.

To ensure that the stringers 90 intersect the ribs 38 at positionswithin the designated tolerance limits, so that the wing panel 30 may befastened to the ribs 38 without the use of shims and without stressingthe wing panel, the stringers 90 must be fastened to the wing skinplanks 54 accurately and consistently. The determinant assembly processis a capable process that enables the use of statistical process controlto detect a trend toward an out of tolerance condition before bad wingpanels 32 are produced so that corrective action may be taken. Accuracyof wing panel fabrication insures that the wing components will cometogether as intended without prestressing the parts and without cosmeticimperfections, and that the assembled wing will function aerodynamicallyas designed. Accurate placement of the stringers 90 on the wing panels30 and 32 makes it possible to use smaller “pad-ups” or thicken areas onthe chords 18 of the ribs 38 or 216 and stringers where the stringersare bolted to the rib chords 92, as shown in FIGS. 6 and 7, instead ofthe wide area pad-ups used conventionally to accommodate the variationin stringer placement. Smaller pad-ups reduces the weight of the ribchords and stringers and increases the load carrying capacity of theairplane.

Coordination holes are drilled in the stringers 90 at the inboard end.Preferably, the coordination holes are drilled when the stringers areinitially fabricated, but they may also be drilled afterward on adedicated fixture or even on the same machine tool 40 on the same orsimilar holding fixtures 42 before the wing skin planks 54 are laid inplace. The specified locations of the stringer fastener holes, at whichthe stringers will be riveted to the wing skin planks, are in themachine tool control program, having been previously down-loaded fromthe data base on which the digital product definition resides. Themachine tool program directs the drill head to the specified locationsfor these fastener holes, typically at one or more of the positionswhere rivets will be installed to secure the stringers to the wing skinplanks to form the wing panels. The stringers can be drilled on amachine tool other than the machine tool 40, whereon the wing skinplanks are positioned and drilled, but doing so introduces a possiblesource of error.

The stringers are fastened to the wing skin planks 54 to secure themtogether in a correctly assembled lower wing panel 32, but the finalfastening of the stringers 90 to the wing skin planks 54 must be donebefore the assembly is a completed wing panel. Numerous wing panelriveting machines are known which can perform the drilling and rivetingoperations with the required accuracy and consistency of quality.

One such machine is illustrated in U.S. patent application Ser. No.08/386,364 entitled “Fastener Verification System” filed on Feb. 7, 1995by Hanks et al. Another such machine is the yoke wing riveter shown inU.S. Pat. No. 5,033,174 issued to Peter Zieve.

In addition, it is contemplated that the riveting of the stringers couldbe done on the same header 60s using upper and lower gantry mounteddrill/rivet units, such as the structure shown in Patent No. 5,231,747.

After all the rivets holding the stringers 90 to the wing skin planks 54are installed, the wing skin is repositioned on the holding fixtures 42by use of coordination holes in the wing panel 30 and the alignment pins82 on the headers 60. Several reference surfaces on the wing panel 30,such as tool balls or reference pins installed in accurately drilledholes in the wing panel, are probed with the probe 84 in the machinetool 40 to determine the actual position of the wing panel 32 on theholding fixtures 42, and the machine program is normalized with theactual position of the wing panel 32 on the fixtures 42. A mill cutteris mounted in the machine tool 40 and the wing panel is trimmed to theexact edge dimensions specified in the digital product definition toensure that the dimensions on the wing are as specified, despite growthin length and width because of the numerous rivets installed during theriveting of the stringers 90 to the wing skin 32. This step is inaccordance with one of the principles of the invention, namely, that theapplication of critical self tooling features in the parts andassemblies are postponed until after the part is distorted by upstreamprocesses. That is, edge machining and other trimming operations couldhave been performed before fastening the stringers 90 to the wing skinplanks 54, but doing so would have required an estimation of theanticipated growth that the assembly would undergo during riveting.These estimations can be quite accurate and have been made successfullyfor many years, but there is always a slight unpredictability factorbecause of the variation in the parameters of the process forinstallation of rivets, lock bolts, Hi-locks and other interferencefasteners, such as exact hole diameter or hole roundness because ofdrill bit wear, slight variations in the countersink depth of the rivethole because of the machine settings, and slight variations in rivetdiameter. Even when these parameters are all well within tolerance, thevariations in the rivet interference they produce in the installed rivetcan accumulate in a large part such as a wing panel to produce variationin the assembly dimensions that can be significant. The effects of thesevariations can be eliminated by scheduling the application of criticalfeatures on the parts and assemblies after the distortion by assemblyand manufacturing processes such as installing interference fasteners,heat treating, and shot peening.

As shown in FIGS. 8 and 8A, a T-chord 100 is positioned on the inboardedge of the lower wing panel 32 by aligning coordination holesaccurately drilled in an outboard flange 102 of the T-chord withcorresponding coordination holes drilled in the inboard edge of the wingpanel. Accurate placement of the T-chord is important because, in part,it determines the position of the wing on the airplane, and also becausea vertical flange 104 on the T-chord must align in a flat vertical planewith corresponding flanges on other wing structure, to be describedbelow, for attachment of a side-of-body web 106. The web is sealed tothe flanges and is the inboard structure of the wing fuel tank, so theflanges must align with a small tolerance for proper fitting of theside-of-body web 106.

A paddle fitting 108 is positioned over the T-chord flange 102 byaligning coordination holes predrilled in the paddle fitting with thealigned coordination holes through the T-chord flange and wing skin. TheT-chord and paddle fitting are clamped in place using temporaryfasteners through the coordination holes, and full sized fastener holesare drilled through the assembly. A series of vertical vanes 110 on thepaddle fitting is positioned to lie flush against a flat face on each ofthe lower wing stringers 90, and is clamped thereto and back drilledwith full sized fastener holes. The paddle fitting 108 and T-chord 100are disassembled and deburred, and the holes are coldworked to improvedtheir fatigue life, since the T-chord and paddle fitting are part of theconnection of the wing to the wing stub in the airplane fuselage, andthe connection experiences high stress and fluctuating loads. TheT-chord 100 is coated with sealant and is attached to the inboard edgeof the lower wing panel 32 with bolts 112.

The upper wing panel 30 is the last major subassembly to be added to thewing box, and is installed only after the lower wing box has been built.However, the upper wing panel 30 may be built in parallel with the lowerwing panel 32, or whenever the scheduling best coincides with theavailability of manpower. The upper wing panel 30 is very similar in itsconstruction and assembly processes to that of the lower wing panel 32,so it will not be separately described. One exception is the design ofthe component, called a “double-plus chord” 116, by which the wing isattached at its upper wing panel to the wing stub (not shown) in theairplane fuselage. The double-plus chord 116, also shown in FIG. 8, hasupper and lower vertical flanges 118 and 120 which are fastened to thefuselage skin 122 and to the side-of-body web 106, respectively, whenthe wing is attached to the airplane. Two additional vertically spacedsideways projecting flanges 124 and 126 on each side of the double-pluschord 116 engage the wing stub on the inboard side and receive theinboard end of the upper wing panel 30 on the outboard side of thedouble-plus chord. Coordination holes drilled through the upper wingskin and the stringers 90 at the inboard end align with correspondingcoordination holes drilled in the sideways projecting flanges 126 toposition the upper side of the wingbox properly when it is attached tothe wing stub.

In-spar ribs 38 are fabricated and brought to the wing major assemblyarea for assembly into the wing. Ribs 38 are of basically two types:machined ribs and built-up ribs. Machined ribs are machined out of asolid slab of aluminum and have the benefit of greater dimensionalaccuracy. However, until the advent of high speed machining which makespossible the machining of thin walled structures without the problem ofdistortion due to localized heating from the cutter, it had beennecessary to make the structure heavier than required by engineeringanalysis for anticipated loads, to prevent heat distortion of the thinwalls. The greater weight and the greater cost of the machinedcomponents has delayed the acceptance of monolithic machined ribs andother components, but new procedures are being developed to solve theproblems that will permit wider use of these components in airplanestructures.

Built-up ribs 214, shown in FIGS. 6 and 7, are made using thedeterminant assembly processes of this invention by a process similar tothat used to make wing spars, disclosed in the first-mentioned U.S.Provisional Application and in our companion application entitled“Determinant Spar Assembly” filed concurrently herewith. A rib web 216is cut from a sheet of aluminum using a machine tool such as agantry-mounted machine tool programmed to drive a cutter around theprofile of the rib web 216. The rib web profile data is input to themachine tool drive program from the engineering authority responsiblefor the digital product definition for the wing and the ribs. Theposition of upper and lower rib chords 218 and 220 on the rib web 216determine the height profile of the rib 214 and hence the chord-wiseprofile of the wing, so they must be accurately positioned on the ribweb 216. The rib chords are accurately positioned on the rib web 214using an accurate positioning and clamping technique such as that shownin the aforesaid Provisional Application and PCT Application entitled“Determinant Spar Assembly”. Fastener holes are drilled through theclamped rib web 216 and rib chords 218 and 220 and interferencefasteners are inserted and secured. After the fasteners are secured andthe rib is fully distorted by the interference fasteners, the rib web216 is end trimmed to the designated length. Coordination holes aredrilled in the two ends of the rib 214 for fastening to the rib posts204 on the wing spars. The locations of the rib post coordination holesare accurately set using a machine tool such as machine tool 40 having acontroller programmed with the coordination hole locations from thedigital rib definition.

Phenolic washers 222 shown in FIG. 7 are bonded to the rib chords 218and 220 at the positions of contact between the rib chords and thestringers 90. These washers are made slightly thicker than needed andare machined to the correct thickness by the machine tool on which theribs are made, or another machine tool of suitable accuracy, to give theribs 38 the correct height as designated in the digital parts definitionof the ribs. The phenolic washers 222 form a bearing surface between theribs 38 and the stringers 90 to accommodate relative movement betweenthe ribs 38 and the wing panels 30 and 32 when the wing flexes duringflight. The washer in this bonded application also serves as a pad ofsacrificial material that can be trimmed to make the height of the ribs38 exactly as specified in the digital parts definition of the ribs.

Wing major assembly is performed on the holding fixtures 42 after thestringers 90 are all fastened to the wing panel 30. The wing panel isplaced, stringer side up, on the holding fixtures 42 and moved intoposition to align at least one coordination hole in the wing panel witha corresponding location hole in one of the headers 60. Conveniently,the wing panel 30 can be floated on an air cushion by connecting asource of air pressure to the lines in the headers 60 that normallysupply vacuum to the suction cups 88. When the wing panel 30 ispositioned accurately on the headers 60, an index pin is insertedthrough the coordination hole or holes in the wing panel and headers 60,and the vacuum cups 88 are connected to the vacuum source 190 to pullthe wing panel 30 against the contact pads 62 on the headers 60 and holdit securely in place.

The wing panel 32, when positioned and secured to the headers 60, isprobed with the touch sensitive probe 84 to locate the coordinatingfeatures such as the tool ball or features machined into the wing panel,such as coordination holes. The predetermined locations of the featureswhich are probed on the panel 30 were recorded in the digital partdefinition, and the actual locations as probed are compared with thepredetermined locations. The machine program is normalized to conform tothe actual position of the panel on the headers 60 so that subsequentoperations are performed accurately on the panel at its actual position.

A program in the controller of the machine tool 40 is initiated to drivea machining cutter around the edges of the wing panel to net trim thepanel 32 to size. Performing this net trim operation after all thestringer fasteners have been installed, instead of beforehand,eliminates the size distorting effect of the many stringer fasteners, sothe dimension of the wing panel 30 is precisely as specified in theproduct definition.

Attaching the Spars and Ribs

The machine tool controller 78 is programmed with the locations ofcoordination holes at the inboard ends of the front and rear spars 36and 34, and holes in the stringers 90 of the lower wing panel 32 forrib-to-stringer bolts, and the machine tool drills these holes, afterwhich the gantry is withdrawn. Sealant is applied to the bottom chord ofone of the spars, and the spar is placed on the edge of the wing panelwith the inboard coordination hole aligned with a coordination holedrilled in the wing panel. The other end of the spar is accuratelypositioned relative to the edge of the wing panel using one or moregauge/clamps 224, shown in FIG. 12, that are accurately machined forthat purpose. A second coordination hole at the outboard end of the wingpanel could also have been used, but it is the edge relationship betweenthe spar and the wing panel that is important at this point, not thelength of the spar. A principle of the invention is to controldimensions that are important, but only while they are important; thespar length is not important at this stage of the assembly, so only theedge relationship of the spar to the wing panel is controlled. Acoordination hole, which would have to register lengthwise of the sparas well as chord-wise from the edge of the wing panel 30, has anunnecessary required degree of precision, so the edge gauges arepreferred over a coordination hole for the outer end of the spar.

The gauge/clamps 224 shown in FIG. 12 each include a body 226 having anupturned flange 228 at one end and a shoulder 230 intermediate the body226. The upturned flange 228 has an end facing surface 232 that isaccurately ground to match the angle of the spar web 132, and theshoulder 230 is accurately ground so that the distance between thefacing surface 232 and the shoulder is exactly the same as the desireddistance between the rear surface of the spar web 132 and the trailingedge of the wing panel 32 at the position set for that gauge/clamp 224.A temporary fastener such as the cleco fastener 234 illustrated in FIG.20 fastens the gauge/clamp 224 to the lower edge of the spar 34 througha hole drilled through the upturned flange 228 and through the web 132and lower chord 136 of the spar 34.

After the spar 34 is pinned to the inboard end of the lower wing panel32 and positioned in the approximate position relative to the edge ofthe wing panel, the gauge/clamps 224 are attached to the lower edge ofthe spar 34 and the shoulder 230 is snugged against the trailing edge ofthe lower wing panel 32. A screw 236 in the end of a pivotally mountedarm 238 of a toggle clamp 240 is tightened against the underside of thewing panel 32 to secure the clamp to the wing panel 32 and hold the spar34 down against the upper surface of the wing skin 56.

Either the front spar 36 or rear spar 34 could be placed first on thewing panel 32. In this first embodiment, the rear spar 34 is placedfirst as a matter of convenience, but in a production operation whereinthe front spar 36 is attached with the leading edge fittings alreadyattached, it may be desirable to attach the front spar first whilesupporting the forward cantilevered weight of the leading edge fittingswith jib cranes.

The first-attached spar is secured in place by clamps and/or temporaryfasteners such cleco removable fasteners. If the front spar with leadingedge fittings is attached first, temporary spar supports such as thetriangular structures 242 shown in FIG. 13 are pinned to the rib posts204 and clamped to stringers 90 on the lower wing panel 32 to react theoverturning moment exerted by the weight of the leading edge fittings,and to hold the spar in position during rib placement.

Certain of the ribs 38 are placed on the stringers 90 and are pinned tothe rib posts 204 through the coordination holes predrilled in the ribposts 204 and the ends of the ribs 38. These are the ribs that would bedifficult to maneuver into position between the front and rear spars 34and 32 after both front and rear spars are attached to the wing panel32. Sealant is now applied to the bottom chord of the other spar and itis laid on the wing panel 32 adjacent the other edge, and thecoordination hole in the inboard end of that spar is aligned and pinnedto the corresponding coordination hole in the wing panel 32. The ends ofthe ribs 38 already in place are pinned to the rib posts 204 of thesecond spar, and that spar is clamped in place at the positiondetermined by the length of the ribs 38. The other ribs 38 are allplaced between the spars and are pinned in place to the spars on theirrespective rib posts 204.

The ribs are fastened to the rib posts by clamping the ribs to the ribposts and removing the coordination pins or temporary fasteners one byone, then drilling and reaming the aligned coordination holes to fullsize for insertion of the permanent fasteners. Alternatively, thecoordination holes could be drilled at nearly full size so they merelyneed be reamed in an operation that is quick and produces quality holesfor the fasteners. As the fastening of the ribs to the spar rib postsproceeds, the temporary spar supports 242 are removed.

The accurate placement of the spars on the edges of the wing panel, andthe accurate attachment of the ribs to the rib posts on the sparsensures that the wing box, formed of the spars, ribs and two wingpanels, will be made accurately in accordance with the digital wingproduct definition. Variations in the dimensions of wing boxes madeusing prior art processes caused difficulties in mounting the controlsurface structures such as leading edge slats and trailing edge flaps,and also caused difficulties in attaching the wing to the airplane.These difficulties are largely eliminated with wing boxes made inaccordance with this invention because of the small tolerances to whichassembly dimensions can be held. The ability to produce wings todesignated engineering tolerances enables for the first time the use ofadvanced tolerancing techniques in wing manufacturing, such as thatdisclosed in PCT Application No. PCT/US96/10757 by Atkinson, Miller andScholz entitled “Statistical Tolerancing”. Economies achieved in thefactory by reduction or elimination of rework alone may justify thecapital cost of the equipment used to practice this invention andscrapping the conventional wing majors assembly tooling.

Rib bolt fasteners 244 shown in FIG. 7 are inserted in predrilled holesthrough the stringer pad-ups and phenolic washers 222 and the rib chordflanges. If the bonded phenolic washers are used, as in the preferredembodiment, they have already been machined to the correct height. Ifnot, separate phenolic washers can be inserted between the stringerpad-ups and the rib chord before the rib bolts 244 are inserted. Theholes predrilled in the rib chord flanges and the stringer pad-ups areslip fit holes to allow limited slip between the rib 38 and the stringer90 on the wing panel 30 when the wing flexes in flight, so thetolerances on these rib bolt fastener holes can be somewhat more relaxedthan the tolerances on the coordination holes which determine partpositions in the assembly.

With the spars 36 and 34, and ribs 38 fastened together and alignedproperly on the lower wing panel 32, the spars are now temporarilyfastened in place. Clamps are applied, which preferably are part of theedge gauges 224 that set the position of the spars relative to theleading and trailing edges of the wing panel 32, as shown in FIG. 12.The clamps generate sufficient interfacial pressure between the sparlower chord 136 and the wing panel 32 to prevent interlaminar burrs fromintruding in the spar/panel interface. Such burrs would interfere with aproper junction between the spar and the wing panel 32 and be verydifficult to remove because of the sealant in the interface. Holes aredrilled for temporary fasteners which are inserted to hold the spar inplace during the permanent fasteners installation. The temporaryfastener holes are drilled undersized so that as the full sized fastenerholes are drilled, any creep in dimensions due to distortion frominsertion of interference fasteners will be removed. Other techniquesfor holding the spars in place while they are being fastened could alsobe used in place of the temporary fasteners.

The spars are now fastened with permanent fasteners in place on theedges of the wing panel 32. The machine tool 40 drills holes in bottomflange 144 of the lower the spar chord 136 from the lower surface orskin side. If the particular machine tool 40 being used is not able todrill from below, it is directed to drill accurate pilot holes fromabove, which pilot holes are used to guide the drilling andcountersinking of fastener holes from below by conventional power tools.Fasteners are inserted and tightened as the drilling proceeds, so anydifferential length growth between the spar and the wing panel iswashed-out as the fastening proceeds along the length of the spar.Fasteners are not inserted in the holes adjacent high stress areas suchas the engine strut fittings, landing gear attachment fittings, and theside-of-body rib because these holes are designated for cold working andit is inadvisable to cold work holes in the presence of wet sealant. Theholes to be coldworked are left until later after the sealant has cured.Use of interference fasteners with a radiused lead-in minimizes the needfor cold working the holes. After the sealant is cured, these holes inhigh stress areas are cold worked, reamed and countersunk and thefasteners are installed and tightened.

Next, the shear tied ribs 38′ are fastened to the lower wing panel 32.As shown in FIG. 14, the shear tied ribs 38′ have projections 246 thatextend between the stringers and terminate in flanges or contact pads248 that engage and are fastened to the underside of the wing skin 56.Pilot holes, predrilled in the pads 248 during fabrication of the sheartied ribs, are used by the mechanic for back drilling through the wingskin 56. It is not necessary to back drill at every pad since thepurpose is to fix the position of the shear tied ribs which are flexibleand, even though fixed at their ends at the rib posts 204 in the spars,can be flexed substantially in the spanwise direction until they arefixed in place to the stringers 90 and/or the wing skin 56. Temporaryfasteners are installed to hold the shear tied rib 38′ in place whilethe permanent countersunk fastener holes are drilled from the underside,that is, from the skin side up through the shear tie pad 248. Thepermanent fastener holes can be drilled by a counterbalanced groundbased drilling unit operated by a mechanic, or preferably are drilled bya machine tool that probes the location of the pilot holes drilled atselected shear tie pads to normalize the digital data from the productdefinition data set with the actual position of the shear tie ribs asindicated by the pilot holes. The machine tool then drills andcountersinks the permanent fastener holes. Prior to installation of thefasteners, the mechanic runs a “chip chaser”, a thin blade-like tool,through the interface between the shear tie rib pads and the wing skinto remove any chips or burrs that may have intruded into that interfaceduring the drilling. The fasteners are inserted from the skin side andsecured by a mechanic on the inside who installs and tightens nuts orcollars on the fasteners and tightens them with the appropriate powertool.

As shown in FIG. 15, three strut fittings 250 are positioned on theunderside of the lower wing panel 32 at the engine strut position andare indexed by way of coordination holes predrilled in the strut fitting250 to coordination holes drilled in the wing panel with the machinetool 40. Internal load fittings 252 are attached to the ribs 38 by wayof accurately drilled coordination holes predrilled during ribfabrication, and the strut fittings 250 are attached to the internalload fittings 252 by fasteners which extend through holes in wing skin56 and aligned holes through the foot of the internal load fitting 252.The forward two strut fittings are fastened to the bottom spar chord byfasteners extending through holes drilled accurately by the machine tool40 using digital product definition data to inform the controller 78 ofthe machine tool 40 as to the locations of those fastener holes. It isimportant that the strut fittings 250 be accurately placed on thewingbox since they support the fuse pins which carry the engine strut onthe wing, and the axis of the fuse pin bores 253 must be properlyaligned to ensure a trouble-free connection of the engine to the wing.The accurate drilling of the coordination holes using data from thedigital wing product definition from the ultimate engineering authorityensures that the engine strut fittings 250 will be accuratelypositioned, thereby eliminating or minimizing any down stream problemsthat would have been produced by mispositioned strut fittings. Temporaryfasteners are inserted in some of the aligned coordination holes to holdthe engine strut fittings and internal load fittings in position whilepermanent fastener holes are drilled. The drilling can be done by handheld power drills, but preferably is done with the machine tool 40. Ifthe holes are to be cold worked, the strut fitting is removed, deburredand the fastener holes in the wing panel, the ribs, and the strutfitting 250 are coldworked and reamed. Faying surface sealant is appliedand the strut fitting is returned to its place and the fasteners areinserted and tightened by the mechanic.

As shown in FIGS. 16 and 17, flap reaction fittings 254 are attached tothe underside of the lower wing panel 32 by aligning coordination holespredrilled in the flap reaction fittings 254 and correspondingcoordination holes in the wing panel, drilled from above by the machinetool 40. These coordination holes can be full sized fastener holes sincethey are not used as pilot holes for back drilling or as temporaryfastener holes. The holes are cold worked and reamed, and the fastenersare installed and tightened to secure the flap reaction fittings inplace. Corresponding flap support fittings 256 are attached to the rearspar 34 during spar build-up by aligning coordination holes 257predrilled in the flap support fittings 256 and the spar web 132 andfastening them together in the aligned position.

Wing close-out involves attachment of the upper wing panel 30 to thewing box frame. Sealant is applied to the flanges of the upper sparchords 134, and the upper wing panel 30 is lifted by crane and loweredonto the assembled spars and ribs of the lower wing box assembly. Theupper wing panel 30 is indexed to the inboard end of the spars by way ofa coordination hole predrilled into the inboard end of the wing panel 30during panel build-up, and a corresponding coordination hole drilledinto the inboard end of the spar, preferably in the terminal end fitting206 during spar build-up. Another pair of coordination features on theupper wing panel 30 and the lower wing box assembly are positionedrelative to each other to fix the position of the upper wing panel 30uniquely on the lower wing box assembly. This other pair of coordinationfeatures could be coordination holes in the edge of the upper wing paneland in the upper spar chord 134 of the front or rear spar 36 or 34 or,preferably, a coordination surface on the front edge of the upper wingpanel and the corresponding edge of the front spar, positioned relativeto each other with an edge locator tool and clamp like the gauge/clamp224 shown in FIG. 12.

The proper positioning of the upper wing panel 30 on the lower wing boxensures that the vertical flange 120 of the double plus chord 116 on theinboard edge of the upper wing panel 30 aligns in a vertical plane withthe vertical flange 104 of the T-chord 100 on the inboard edge of thelower wing panel 32, and also with the inward flanges on the terminalend fittings 206 on the front and rear spars 36 and 34. The alignment ofthese four flanges ensures that the side-of-body rib web 106 will lieflat against all four flanges and will seal reliably and permanentlythereto when it is attached.

The upper wing panel 30 is clamped in its properly indexed positionusing edge clamps like the clamps 224 shown in FIG. 12 or the like. Ribbolts 244 are inserted through predrilled holes in the upper rib chordsand the stringers 90, as shown in FIG. 7. Because the wing box is nowclosed by the upper wing panel 30, access to the interior of the wingbox is through the access openings 258 in the lower wing panel 32. Asmall mechanic crawls into the wing box through the access opening 258between each rib and inserts a rib bolt 244 into the aligned holes inthe upper rib chords and the stringers 90, and tightens the bolts. Theaccurate control over the position of the stringers 90 when the wingpanels are built up makes it possible for the rib bolt holes to bepredrilled and line up with the rib bolt holes in the stringers 90 whenthe upper wing panel is properly positioned on the lower wing box,thereby eliminating the need for drilling the rib bolt holes from insidethe wing box, and also making possible the use of much smaller rib andstringer pad-ups where they are fastened together by the rib bolts.Predrilling the rib bolt holes also has the benefit of accuratelylocating the midportion of the rib, which is somewhat flexible, properlyalong the stringers 90 spanwise on the wing.

With the upper wing panel 30 now firmly fastened to the ribs 38 andclamped to the spars 34 and 36, temporary pilot holes are drilled by themechanic using a hand held power drill from the inside of the wing boxup through shear tie flanges 260 at the top of the rib posts 204 andthrough the wing skin. Reaction force is exerted by the machine tool 40during the back drilling to prevent the upper wing panel 30 from beinglifted off the upper spar chord 134 by the force exerted on the drillduring drilling of the pilot holes. Temporary fasteners are installed inthe pilot holes to hold the wing panel 30 firmly against the spar chord134 while the permanent fastener holes are being drilled so that nochips or burrs intrude into the interface between the spar chord and theupper wing panel. The exact control of the rib height and profile bycontrolling the position of the rib chords on the rib webs ensures thatthe height and contour of the ribs and the spar chords correspondclosely so that the stringers 90 of the wing panel lies on the ribchords and the wing skin lies smoothly over the spar chords without anydiscontinuity that would require shimming.

The machine tool 40 is directed to the spar-to-wing panel fastenerlocations using data from the digital wing product definition whichspecifies the locations and sizes of the fasteners. The fastener holesshould be exactly normal to the surface of the wing skin so that thecountersink axis is also normal to the wing skin at the fastenerlocation. A conical head fastener inserted in a fastener hole properlydrilled normal to the surface of the wing skin at the fastener locationwill lie in the countersink with its head flush with the surface of thewing skin. Such a fastener in a non-normal fastener hole would have oneedge of the fastener's conical head protruding from the countersink, andthe opposite edge recessed below the surface. There is almost nothingthat can make a fastener improperly installed in this way acceptable.Shaving the head removes the protruding edge, but leaves that side ofthe head too narrow. The recessed edge of the head remains recessed andshaving or sanding the wing surface is not an acceptable fix. To ensurethat the fastener holes are drilled normal to the wing surface, aself-normalizing drill head may be used, as shown in U.S. patentapplication Ser. No. 08/785,821 filed on Jan. 8, 1997 by Gregory Clarkentitled “Self-Normalizing Drill Head”.

The machine tool 40 drills and countersinks the fastener holes andinserts the fasteners. A mechanic inside the wing box installs the nutsor collars and tightens the fasteners with a power tool as the fastenersare inserted. The holes are drilled and countersunk in the wing skin,and the holes extend through the top flange on the spar chord. Apressure foot on the drill head exerts a press-up force to assist theclamps and the temporary fasteners in maintaining the pressure at theinterface between the wing skin and the spar chords to prevent chips andburrs from intruding into that interface. The press-up force alsoassists in squeezing out any excess sealant resulting in very littlesealant on the chips, so they may be vacuumed away without fouling thechip vacuum system with sealant. Temporary fasteners may be installed inthe holes that require coldworking until the sealant cures, after whichthe holes may be coldworked and reamed, and the permanent fastenersinstalled.

The upper wing panel 30 is fastened to the shear tied ribs 38′ as shownin FIG. 14 by drilling fastener holes from above the wing skin with themachine tool 40, using the digital product definition to inform themachine tool controller of the location of the shear tie pads 248 underthe upper wing skin. Because of the flexibility of the ribs, it may bedesirable for a mechanic to back drill pilot holes through predrilledpilot holes in selected shear tie pads 248 and install index head tackfasteners to fix the position of the intermediate portions of the sheartie ribs 38′ against flexing in the spanwise direction. The machine tool40 can then probe for the index heads of the tack fasteners andnormalize the machine tool program with the actual position of the sheartied ribs 38′ based on the position of the index heads. The machine tool40 drills and countersinks full sized fastener holes from above theupper wing skin while a mechanic inside the wing box runs a chip chaserbetween the shear tie pads 248 and the inside surface of the wing skin.The machine tool 40 inserts the fastener while the mechanic inside thewing box places the nuts or collars and tightens the bolts with theappropriate power tool.

Aileron hinge ribs 130 are attached to the rear spar 34 for supportingan aileron hinge rod in bushings spaced to the rear of the rear spar. Itis important for the smooth and trouble free operation of the aileronthat the bushings in the ends of the aileron hinge ribs be alignedaccurately on a single axis parallel to the rear spar. Because of thelength of the aileron hinge ribs 130, a small discrepancy in itsplacement is magnified to a large deviation from the intended positionof the hinge bushing at the end of the hinge rib. It was found that,even when the aileron hinge ribs were attached with the best possibleaccuracy while the spar 34 was being built up, the small distortion thatwas produced during final wing box assembly was sufficient to createunacceptable displacements of the ends of the hinge ribs so that theywere no longer axially aligned. Therefore, in the practice of thisinvention, the attachment of the hinge ribs is scheduled for an assemblystage after the majority of the distorting events are finished.

Another factor influencing the positional accuracy of the hinge bushingon the installed hinge rib 130 is the effect that minute variations ofpositioning of the proximal end, or attaching end, of the aileron hingerib 130 have on the position of the hinge bushing. Even whencoordination holes are drilled very accurately in the spar web and inthe proximal end of the aileron hinge rib, very small local variationsin the flatness of the facing surfaces, variations in theperpendicularly of the hinge rib to its distal end mounting plate, andother small such variations can have a significant effect on theposition in space of the hinge bushing after the rib is attached to therear spar.

To avoid all these problems in accordance with this invention, the hingebushing in the end of the hinge rib 130 is set at its critical positionin space, and the hinge rib is attached to the spar where it contactsthe spar web. This simply avoids the difficulties of trying to controlall the factors that influence the position of the hinge bushing inspace. The controller 78 of the machine tool 40 directs the machine tool40 to position a mounting pin 262, held by the machine tool 40 as shownin FIG. 18, in space at the position to the rear of the rear sparspecified by the digital product definition as the location of the hingebushing. The hinge bushing in the distal end of one of the hinge ribs isslipped onto the mounting pin 262, locating it accurately in spaced atits position specified by the digital product definition, and theproximal end of the hinge rib is attached to the spar web at theposition determined by the position in space of the hinge bushing.

The side-of-body web 106 is positioned on the vertical flange 120 of thedouble-plus chord 116 and the vertical flange 104 of T-chord 100, and onthe two sideways flanges on the spar terminal end fitting 207 usingcoordination holes predrilled into the side-of-body web 106 and the fourflanges, as shown in FIGS. 8 and 8A. Temporary fasteners are installedto hold the side-of-body web 106 in place while full size fastener holesare drilled through the web and the four flanges. The web 106 is removedand the holes deburred, and the faying surface of the web is coated withsealant. The coated web is replaced on the flanges and fasteners areinserted through the holes. A mechanic inside the wingbox installs nutsor collars on the fasteners and tightens them with the appropriate powertool.

The determinant assembly process is not limited to assembly of the majorcomponents in the horizontal or lying down position, illustrated in FIG.3, with the waterline of the wing lying horizontally. Another assemblyorientation is the spar-based vertical or “on-edge” orientation, withthe waterline of the wing oriented vertically as shown in FIG. 19, usingthe rear spar as the base member on which the assembly is built. Therear spar is supported on a spar support structure 264 with the spar webin the horizontal position. This embodiment uses the rear spar 34′ asthe base sub-assembly to which the ribs and wing skins are attached. Thespar support structure 264 holds the rear spar accurately to itstheoretical shape while the assembly process proceeds. Ribs 38 arelocated to the rear spar 34′ by aligning coordination holes in the ribsthat are common to the rib posts 204. Temporary supports are attached tostabilize the ribs 38 until they are attached to the front spar 36′. Aseries of holding fixtures 266 is provided to hold the front spar 36′ atthe theoretical waterline position relative to the rear spar 34′. Theholding fixtures 266 permit adjustment of the front spar 36′ up and downsince the distance between the rib coordination holes determines thechordwise distance between the front and rear spars, just is it does forthe embodiment of FIG. 1. After all the fasteners are installed tosecure the ribs to the spars, the temporary rib supports are removed.

The upper wing panel is positioned against the inner wing structure andaccurately positioned in place by inserting alignment pins through acoordination hole in the inboard end of the wing panel. Thiscoordination hole is common to the inboard end of the rear spar 34′.Outboard and intermediate secondary index holes in the rear spar provideadditional location but are allowed to have some misalignment in thespan-wise direction, for example, by using differential undersized holesor a slot in one part. Wing panel fixturing is designed to support theweight of the wing panel since the alignment pins through thecoordination holes would not normally be designed to support a load ofthat magnitude. Since the panel fixture is not the sole authority forwing panel location, it is provided with adjustment mechanisms such asindependent jacks and the like to facilitate alignment of thecoordination holes in the wing panel and the spars.

After the wing panel is strapped or pulled against the ribs and frontspar, full-sized fastener holes are match drilled in the wing skin, thespar and the ribs. The shape of the wing is determined by the shape andplacement of the ribs. The wing skin is allowed to conform to the ribsby starting from the rear spar and wrapping the wing skin around theribs by progressively installing fasteners until the wing skin meets thefront spar. No coordination holes common to the front spar and theleading edge of the wing skin are needed, and the wing design allows asmall payoff between the fixed leading edge and the wing skin.

After the fastener holes are drilled, the wing panel is separated fromthe ribs and spars and is deburred, cleaned, fay sealed and relocatedagainst the ribs and spars. Fasteners are installed and tightened asdescribed earlier. A numerically controlled track drill, machine tool orthe like is used to drill holes in the skin common to the spar, therebyeliminating the use of drill templates now in common use in conventionalwing manufacturing facilities. The lower skin is located and indexed tothe rear spar just as the upper skin was. Nacelle, landing gear, flaptracks and other major fittings are located using light weight toolsthat pin to localized key coordination holes in the skin.

A spar based horizontal assembly technique is illustrated in FIG. 20.This technique allows access to both top and bottom sides of the wingand potentially could permit simultaneous operations on both sides forfaster throughput and higher production rates.

The front and rear spars 34 and 36 are mounted on and supported by sparsupports 270 and 272 carried by fixed upright columns 275. The sparsupports 270 and 272 slide laterally in guides or linear bearings in thecolumns 275 to accommodate different sizes of wing for different modelairplanes. The lateral freedom of movement also allows the spars toself-adjust to the lateral spacing between spars determined by thecoordination holes drilled in the ends of the in-spar ribs.

Two laterally spaced rails 277 are mounted on rigid longitudinal beams279 supported atop the columns 275. An upper gantry 280 is mounted forlongitudinal traversing movement on the rails 277 under control of thecontroller 78 by traversing motors 282. A laterally traversing plate 286mounted on rails 288 fastened to the gantry 280 is driven by engagementof a ball nut 290 with a ball screw. The ball screw 292 is driven by aservomotor mounted behind the plate 286 under control of the controller78. A vertical arm 295 mounted on linear bearings and driven by a drivemotor has a wrist 297 that can tilt to a desired angle and can rotateabout the vertical axis of the arm 295. The wrist has a gripper thataccepts a mechanical and power connection for an end effector so the arm295 can position an end effector at the desired locations for drilling,hole measuring and conditioning, and fastener insertion.

A lower gantry 300 is mounted for longitudinal movement on rails 302mounted on a shoulder 304 adjacent the inside edges of the columns 275.The gantry 300 has an arm 308 which is mounted like the arm 295, exceptthe operating end is at the top end instead of the bottom end as for thearm 295 of the gantry 280. Otherwise, the gantries 280 and 300 arebasically the same.

In operation, the spars 34 and 36 are loaded onto the spar supports 272and the ribs are indexed to the rib posts on the spar and fastenedthereto by temporary fasteners through the coordination holes. The upperand lower gantries are used to drill the fastener holes, and the ribsare removed, deburred and sealant is applied to the faying surfacescommon to the rib posts. The ribs are repositioned and the end effectoron the gantries 280 and 300 inserts the fasteners which are secured byworkers following behind the gantries.

After all the ribs are attached, the lower gantry 300 is moved to aparking position at one end of its longitudinal travel beyond the wingposition, and a lower wing panel 32 is transported by crane to a gurneysupported on the same rails 302, and moved into position beneath thespars 34 and 36 and the in-spar ribs 38 on the gurney. The lower wingpanel 32 is elevated to the undersurface of the spars 34 and 36 and thein-spar ribs 38 with a series of vertically telescoping supports and isindexed to the spars by alignment of predrilled coordination holes inthe panel 32 and the spars 34 and 36. The wing panel is temporarilysecured in place with straps around each rib and the verticallytelescoping supports are retracted, clearing the way for the lowergantry 300 to move in and begin drilling fastener holes for attachingthe wing panel 32 to the spars and ribs. The upper gantry arm 295 can bepositioned opposite to the arm 308 to provide a reaction clamping forceto prevent the feed force on the drill in the end effector in the arm308 from lifting the rib or spar chord flanges away from the wing panel32 when the drill breaks through the wing panel, which could allowinterlaninar burrs to intrude between the surfaces. It is thus possibleto apply sealant when the wing panel 32 is first positioned since thereis no need for the usual deburring step.

After the lower wing panel 32 is attached, the upper gantry 280 is movedto a parking position beyond the wing position and upper wing panel 30is transported by overhead crane directly to its intended position onthe spars and ribs. The upper wing panel 30 is indexed to its correctposition by aligned coordination holes predrilled in the wing panel anddrilled in the spars 34 and 36 by an end effector held by the gantry arm295. Index pins in the aligned coordination holes lock the wing panel inthe proper position, and the gantry arm 295 moves to the positionsdesignated by the machine program 68 to drill fastener holes. Dependingon the stiffness of the spar chord flanges and the rib chord flanges andthe drilling parameters, such as feed force, it may be necessary todeburr the fastener holes by lifting the wing panel 30 high enough toopen access to the underside of the wing panel 30 and the top side ofthe spar and rib chords for the deburring operation. Sealant is appliedand the panel is repositioned and the fasteners are inserted and securedas explained above.

End trimming of the spars and wing panels can be performed with routercutters in end effectors held by the arms 295 and 308. Coordinationholes for the other components mentioned above are drilled by the gantryend effectors for attachment after removal from the apparatus. Theaileron hinge ribs can be attached using pins held at the correct pointin space by the gantry end effectors.

It is contemplated that two support fixtures shown in FIG. 20 could bepositioned end-to-end so that the gantry positioner/machine tools couldbe at one end working on assembling the wing while workers are at theother end removing an assembled wing and setting up the components forthe next wing to be assembled.

A system is thus disclosed which is usable for assembling airplane wingsubassemblies into a full airplane wing with a high degree of precisionand repeatability. The determinant assembly concept embodied in thisdisclosure utilizes the spatial relationships between key features ofdetail parts and subassemblies, as defined in the digital design andrepresented by coordination holes and other coordination features putinto the parts and subassemblies by a numerically controlled tool, usingoriginal part design data from the engineering authority, to control therelative location of detail parts in subassemblies and the relativerelationship of subassemblies to each other, making the parts andsubassemblies self locating. This concept eliminates the need fortraditional hard tooling used for decades in the airframe industry andfor the first time enables assembly of large, heavy, flexible andsemiflexible mechanical structures wherein the contour of the structureand the relative dimensions within the structure are determined by theparts themselves rather than the tooling.

Freed in this way from dependence on fixed tooling, the wing can now bebuilt to accommodate distortion created by manufacturing processes, suchas interference fasteners and cold working, so that attachment ofcritical features on the wing at precisely accurate positions specifiedby the engineering design can be scheduled in the manufacturing processafter distortion by the upstream processes which would have affectedtheir position or orientation on the wing. The factory can nowmanufacture wings of any shape and size for which engineering data isprovided, within the physical range of the CNC machine tools, and do sofaster and with far greater precision than was possible with fixedtooling. The cost of building and maintaining the conventional wingcomponent and wing major tooling, and the factory floor space for suchfixed tooling, no longer need be amortized and factored into the priceof the airplane, and it is now possible to build wings customized tomeet the particular requirements of particular customers.

Obviously, numerous modifications and variations of the system disclosedherein will occur to those skilled in the art in view of thisdisclosure. Therefore, it is expressly to be understood that thesemodifications and variations, and the equivalents thereof, will beconsidered to be within the spirit and scope of the invention as definedin the following claims, wherein we claim:
 1. A method of manufacturinga wing, comprising: positioning a wing panel on a fixture and holdingsaid panel immobile on said fixture; accurately placing criticalcoordination features in said wing panel and in two wing spars using anumerically controlled machine tool running on part programsincorporating digital wing product definition data from an engineeringdata authority, said critical coordination features being placed in saidwing panel at locations having predetermined relationships withcorresponding coordination features in said wing spars when said sparsare accurately located in predetermined positions, spaced chord-wisefrom each other on said wing panel, specified by said digital wingproduct definition against said wing panel with said critical featuresin said spars and said wing panel positioned in said predeterminedrelationship to each other; fastening said wing spars in fixed relationrelative to said wing skin in said predetermined position; placingrib-to-spar critical coordination features in a plurality of wing ribsand in said spars using numerically controlled machine tools running onprograms incorporating digital wing product definition from anengineering data authority, said ribs being accurately located in apredetermined position specified by said digital wing product definitionrelative to said wing spars when said rib-to-spar critical features insaid ribs and said wing spars are positioned in a predetermined relationto each other; fastening said wing ribs to said wing spars in saidpredetermined position; drilling a plurality of stringer-to-chordcoordination holes in lower wing skin stringers attached to a lower wingskin and in a lower spar chord using a numerically controlled machinetool running on a program incorporating said digital wing productdefinition data from said engineering data authority, said lower wingskin being accurately located in a predetermined position specified bysaid digital wing product definition relative to said wing spars whensaid stringer-to-chord critical features in said ribs and said wingspars are positioned in a predetermined relation to each other;fastening said wing stringers and said wing spars together in saidpredetermined position; locating a reference fixture spatially relativeto a rear spar at a position corresponding to a predetermined positionof a hinge axis specified by said digital wing product definitionrelative to said rear wing spar, using a numerically controlled machinetool running on a program incorporating said digital wing productdefinition data from said engineering data authority; and sliding ahinge barrel attached to a distal end of a hinge rib onto said fixture,and fixing a proximal end of said hinge rib to said rear spar at aposition such that said hinge axis remains at said predetermined hingeaxis position, said hinge axis being accurately located in apredetermined position specified by said digital wing product definitionrelative to said wing.
 2. A method of making an airplane wing with upperand lower outer mold lines corresponding closely with designspecifications for said wing, said wing having upper and lower wing skinpanels, each with inner and outer contour surfaces, comprising:positioning a plurality of headers on a bed of a machine tool, saidheaders when positioned on said machine tool bed having upper contourscoinciding closely with said lower outer mold line of said wing;indexing said lower wing skin panel on said headers and supporting saidlower wing panel thereon with a lower outside surface thereof coincidingclosely with said outer contour surface; machining coordination featuresin said lower wing panel on said machine tool using digital wing productdefinition data from an engineering authority for said wing to programsaid machine tool as to the location of said coordination features;applying sealant to outer surfaces of lower flanges of front and rearwing spars and accurately positioning said front wing spar on said lowerwing panel adjacent a front edge thereof, and positioning said rear wingspar on said lower wing panel adjacent a rear edge thereof usingcoordination features on said spars and said coordination features onsaid lower wing panel; fastening one of said spars in a fixed locationto said wing panel adjacent one edge thereof, and fastening the other ofsaid spars at one end thereof adjacent the other edge of said wingpanel; drilling coordination holes in the end portions of a multiplicityof in-spar ribs and corresponding coordination holes in a multiplicityof rib posts attached to said spars in positions corresponding to thedesired positions of said in-spar ribs in said wing, said coordinationholes, said rib post coordination holes and said rib end coordinationholes having been accurately drilled by a machine tool programmed withhole location data from said digital wing product definition data fromsaid engineering authority for said wing, said rib post coordinationholes and said rib end coordination holes being positioned to positionshear tie surface and stringer contact surfaces on said in-spar ribs ata position such that said wing panel outer contour surface willcorrespond closely with the desired wing contour when said wing panel isfastened to said in-spar ribs; fastening said in-spar ribs to said ribposts at locations determined by registry of said rib post coordinationholes and said rib end coordination holes; fastening said front and rearspars to said lower wing panel by drilling holes through said wing paneland through said spar flanges, inserting fasteners through said holes,and securing said fasteners in said holes; and fastening said lower wingpanel to said ribs and to said spars to produce a lower wing boxassembly; and positioning an upper wing panel over said lower wing boxassembly and fastening said upper wing panel to said ribs and saidspars.
 3. A method of making a wing as defined in claim 2, furthercomprising: fastening said wing panel to said shear ties by directingsaid machine tool to a position vertically aligned with a flange on saidshear tie; drilling a hole through said wing panel and said shear tieflange with a drill bit in said machine tool; and inserting and securinga fastener in said hole; whereby said directing step includesdownloading data from said digital wing product definition to acontroller for said machine tool and using said data to inform saidmachine tool controller of said fastener hole locations.
 4. A method ofmaking a wing as defined in claim 2, wherein: fastening said rib chordsto said rib web with interference fasteners; at least one of saidrib-to-spar coordination holes are drilled after said rib chords arefastened to said rib web; whereby said rib web is distorted byinterference fasteners before the chord-wise distance between said frontand rear spars is set by said rib-to-spar coordination holes on said oneend of said rib is drilled.
 5. A method of making a wing as defined inclaim 2, further comprising: machining said headers with said machinetool to produce said upper contours using data from said digital wingproduct definition data from said engineering authority for said wing toprogram a machine tool controller that controls operation of saidmachine tool.
 6. A method of making a wing as defined in claim 2,further comprising: attaching aileron hinge ribs to said rear spar bypositioning a pin held by said machine tool at a location determined bysaid digital wing product definition data from said engineeringauthority for said wing on an aileron hinge axis; sliding a hingebushing on a distal end of said aileron hinge rib onto said pin toaccurately position said distal end of said hinge rib at its designatedposition; fastening said hinge rib to said rear spar at a position tomaintain said position of said distal end of said rib after said pin isremoved; and removing said pin from said hinge bushing.
 7. A method formanufacturing a product, comprising an assembly of detail parts, tocorrespond within designated tolerances of a digital product model in adigital product definition, comprising: generating a digital definition,including a digital model, of each of said detail parts, said detailparts digital models, when assembled digitally, corresponding to saiddigital product model; manufacturing said detail parts in accordancewith said detail part definitions; assembling said detail parts intosaid product by: a. placing a first major subassembly of said detailparts on a support surface of a fixture, oriented in a predeterminedspatial orientation on said support surface; b. measuring the actualposition of said first major subassembly to determine the actualposition thereof on said fixture; c. normalizing the orientation of saiddigital model to correspond to said actual position of said first majorsubassembly on said support surface; d. positioning other parts relativeto said first major subassembly in accordance with said digital modeland fastening said other parts into said assembly to produce saidproduct.
 8. A method as defined in claim 7, further comprising: trimmingsaid support surface with a trimming tool under control of a CNCcontroller to an accurate profile defined in said digital productdefinition, using data from said digital product definition to programsaid controller, before placing said first major subassembly on saidsupport surface.
 9. A method as defined in claim 2, wherein: saidpositioning of said other parts relative to said first major subassemblyincludes machining coordinating features in said other parts and placingsaid parts with said coordinating features at a predeterminedrelationship to each other to position them said other parts accuratelyrelative to each other; said machining step includes programming a CNCcontroller of an accurate machine tool to direct a cutter with preciseaccuracy to positions, designed as coordinating features in said digitalproduct definition and on said parts, to cut said coordinating features.10. A method as defined in claim 7, wherein: said fastening includes a)drilling fastener holes through abutting portions of said other-parts;and b) inserting interference fasteners in said holes; wherebyelimination of dimensional variations due to accumulated distortionproduced by said fastener insertion is facilitated by scheduling saidfastener insertion in an assembly sequence prior to a final trimmingoperations.
 11. A method as defined in claim 10, wherein said drillingincludes: transmitting said digital product definition to a CNCcontroller of a machine tool; driving a drilling head on said machinetool accurately to fastener locations specified in said digital productdefinition; pressing said other parts together to prevent burrs fromintruding into an interface between said parts at said fastenerlocations; and drilling said holes.
 12. A method as defined in claim 7,further comprising: assigning a level of priority to each of said detailparts based in part on an importance of dimensional accuracy of saiddetail parts to the dimensional accuracy of said assembly; and buildingsaid detail parts to a dimensional accuracy commensurate with said levelof priority; and maintaining said dimensional accuracy of said detailparts for only so long as said dimensional accuracy is important to saiddimensional accuracy of said assembly.